Add runtime command to show a specific output channel

[dhruvisompura]

In #5999, we added a way for users to view session metadata and view logs. The popup has a button to show logs (the <language+version>: Kernel channel). When clicked, the user is shown the logs for their session in the output pane. The underlying mechanism that allows us to do this is the showOutput runtime command in the language packs.

Each language pack has multiple output channels and we are interested in adding a button to show the user the following channels:

• Language Pack
• Language Console

We will need to add a new runtime command that the UI can invoke to show a specific output channel.

The PR that added the showOutput command to the positron API: ef0802b).

[jmcphers]

Note that these output channels are specific to the current implementation of the R and Python language packs -- they both use Jupyter kernels and a supervisor process that populates a Console and Kernel channel. However this should be considered an implementation detail, and not all language packs should be required to have these output channels. A couple of ways we could go about this:

• these methods could be optional; we have a set of well known channels and the runtime exposes commands to show the ones that it implements
• the runtime could instead have a method that allows Positron to ask it to return a list of its output channels, which Positron could show in the UI without any prior knowledge